Prosthetic dentures currently in use typically consist of a baseplate of hard poly(methyl methacrylate) which supports the artificial teeth needed for chewing and for esthetics. Many patients have difficulty tolerating a hard denture so there is a need for a soft denture liner affixed to the denture base to cushion the soft tissue. A number of criteria have been established for materials to be useful as denture liners, notably non-toxicity and non-allergenicity. The best materials should be permanently resilient, inert, cleanable, and substantially water-insoluble, and have low water-sorption characteristics and good tensile strength. While softness is desirable for comfort, the liner material must be sufficiently firm to displace the soft tissues of the mouth and to allow grinding of the denture periphery to avoid creating sore spots; additionally, the liner material must be permanently bondable to the denture base material. It is also highly preferably from a practical standpoint that the lined denture be capable of fabrication under conditions generally found in dental laboratories, or in a dentist's office, avoiding extremes of temperature and pressure conditions, or the use of special equipment.
Several liner materials have been proposed which satisfy these criteria sufficiently to be useful, such as silicone rubber, plasticized poly(methacrylates), polyurethanes, and polyvinyl chlorides. An especially useful liner material is disclosed in U.S. Pat. No. 4,251,215 issued on Feb. 17, 1981 to May et al., comprising phosphonitrilic fluoroelastomer (poly(fluoroalkoxy)phosphazene) which exhibits particularly good resiliency, water-sorption, and biocompatibility characteristics. The fluoroelastomer liner materials exemplified therein, however, have been found to be somewhat deficient with respect to tensile strength, hardness, and bondability to denture base material, as compared to the theoretical ideal. Further, the process for forming the denture as described in the May et al. patent is a two-step process which requires the liner and denture base to be separately cured, and additionally requires the use of strong bonding agents, as well as the use of temperatures in excess of 100.degree. C. (boiling point of water at atmospheric pressure) for curing the liner. The fabrication of this prior art composite denture thus requires somewhat elaborate equipment, and cannot be conveniently accomplished in an average dental office or laboratory.